Radioactive medical devices for inhibiting a hyperplastic response and method of making radioactive medical devices

ABSTRACT

This invention involves radioactive medical devices for inhibiting an undesirable hyperplastic response in biological tissue, and a method for making the radioactive medical devices. In a preferred embodiment, a medical device for inhibiting a hyperplastic response in biological tissue generally comprises polymeric hydrocarbon molecules forming the medical device and a salt or an acid of a radioactive isotope occluded within the polymeric hydrocarbon molecules. Also in a preferred embodiment, a method of creating a medical device according to the present invention comprises: providing a first solvent in a container; introducing a salt or an acid of a radioactive isotope into the first solvent; introducing a second solvent into the first solution so as to form a second solution; and introducing the medical device into the second solution, wherein the ionic components of the radioactive isotope migrate into the molecular structure of the medical device.

FIELD OF THE INVENTION

The present invention relates generally to medical devices and, moreparticularly, to a radioactive medical device having beta radiationemitting capabilities for inhibiting an undesired hyperplastic responseto the healing of biological tissue, and a method for making and usingthe devices.

BACKGROUND OF THE INVENTION

In patients with arterial occlusive disease, vascular surgeons usesutures to anastomose autogenous vein, prosthetic grafts, or arteries toother arteries in order to bypass around or replace diseased arterialsegments. At virtually all anastomotic sites between the arteries andautogenous vein, or prosthetic grafts, a condition of rapid cellulargrowth termed “intimal hyperplasia” may occur.

Intimal hyperplasia is the usual response to blood vessel injury. Thisrapid cellular growth, as a response to injury of the blood vesselcellular lining, begins to narrow the opening between the vessels and/orgraft to the point where an occlusion may occur. More specifically,intimal hyperplasia forms as a result of smooth muscle cellproliferation, migration, and extracellular matrix deposition. Theinteraction of platelets, macrophages, growth factors, and cytokinesplays an important role in the process. Intimal hyperplasia is theprimary cause of “restenosis” (narrowing) in the first year aftervascular bypass operations and may cause indwelling venous catheters toocclude as well. Usually, the patient must have another operation torevise or replace the occluded graft. If a major vein occludes (e.g.jugular or subclavian) massive edema of the upper extremity, face andneck may occur and if an artery occludes, it could possibly lead topotential limb loss.

Of course, intimal hyperplasia is merely a subset of a larger probleminvolving hyperplasia resulting from smooth muscle cell proliferation,migration, and extracellular matrix deposition. In general, whenbiological tissue begins grafting, or healing, an undesirablehyperplastic response may occur. It would be desirable to limit, or evenprevent such an unwanted hyperplastic response.

The most frequently performed prosthetic graft operation is an arterialto venous conduit for dialysis in chronic renal failure patients. Renaldialysis patients require repetitive angioaccess to this arterial—venousgraft for dialysis to rid their system of toxins. The most commonly usedgraft for dialysis is a synthetic graft made from teflon or ePTFE(expanded polytetrafluroethylene). Unfortunately, these grafts rapidlyfail and have a primary occlusion rate of 15% to 50% during the firstyear, with a mean patency of only 15 months. This failure in most casesis due to the development of intimal hyperplasia at the venousanastomosis. Again, there is a strong desire in the art to prevent thisunwanted hyperplastic response.

Both of the examples of tissue grafting outlined above, surgery as aresult of arterial occlusive disease and an arterial to venous conduitfor dialysis, prescribe the use of a suture to assist the healing ofbiological tissue. However, there are several devices currently used inthe medical field for assisting the grafting of biological tissue. Forexample, sutures, “patches” and meshes are used to hold tissues in placeand give the tissues time to heal. Similarly, stents come in a varietyof configurations for supporting blood vessel walls in an attempt toinhibit stenosis of the vessel.

Surgical sutures are used to bring together ends of biological tissueand hold them in place until the joining tissues have time to heal. Asanother example, in some types of medical operations, medical personnelmay use “patches” or meshes to hold damaged tissue in order to give thetissue appropriate time to heal. These “patches” function in a mannersimilar to sutures, but are much quicker to apply and may be effectivewhere a suture would not be appropriate. Just as with vascular bypassoperations and the restenosis that may occur, the tissue held by the“patch” or mesh may also exhibit signs of hyperplasia that areundesirable, if not harmful.

In recent years, studies have been conducted in animal models whosevessels have undergone angioplasty. It was found that the vesselsresponse to injury from balloon angioplasty is similar to that observedat suture anastomotic lesions. Studies conducted at Emory University,Atlanta, Ga., U.S.A., and Vanderbilt University, Nashville, Tenn.,U.S.A., suggest that restenosis results primarily from the migration andrapid proliferation of a smooth muscle type cell after balloonangioplasty. It has been demonstrated by these groups that very lowlevels of beta-particle irradiation introduced to the site of injuryfollowing angioplasty markedly inhibits smooth muscle cell proliferationand or migration. Numerous other studies have been conducted which havedemonstrated and substantiated these early findings.

U.S. Pat. No. 5,897,573, filed Apr. 22, 1997, dealt with the problem ofunwanted hyperplastic response in biological tissue by suggesting theirradiation of a suture material prior to its use in a patient. U.S.Pat. No. 5,897,573 describes how a low-level beta-emitting radioisotopemay be incorporated into the chemical structure of suture material inorder to inhibit an unwanted hyperplastic response. U.S. Pat. No.5,897,573, filed Apr. 22, 1997, is hereby incorporated by reference asif fully set out herein.

Similarly, U.S. Pat. No. 6,042,600, filed Jan. 25, 1999, dealt with theproblem of unwanted hyperplastic response in biological tissue bysuggesting the irradiation of various medical devices before use in apatient. U.S. Pat. No. 6,042,600 was a continuation in part of U.S. Pat.No. 5,897,573. U.S. Pat. No. 6,042,600 describes how a low-levelbeta-emitting radioisotope may be incorporated into the chemicalstructure of a medical device. U.S. Pat. No. 6,042,600, filed Jan. 25,1999, is hereby incorporated by reference as if fully set out herein.

Both of the two above-described patents generally prescribe chemicallybonding the radioactive element to the structure of the medical device.However, there may be situations where it is not desirable to alter thechemical structure of the medical device to be used. Additionally,certain isotopes may not readily lend themselves to chemically attachingthemselves to the molecules of the medical device.

Thus, there exists a need in the art for a radiation-emitting medicaldevice where the radioactive element is not chemically bonded to thestructure of the device. There also exists a need in the art for amethod of making such medical devices. The invention described belowremedies any shortcomings of the prior art.

SUMMARY OF THE INVENTION

Generally described, the present invention provides a radioactivemedical device having beta radiation emitting capabilities forinhibiting an undesired hyperplastic response to the healing ofbiological tissue, and a method for making and using the devices. It isknown that smooth muscle cell proliferation may be inhibited by varyingdegrees and types of radiation, particularly low level beta radiation.This knowledge is exploited by the radioactive medical devices andmethod described herein.

In a preferred embodiment, a method of creating a medical device thatinhibits a hyperplastic response in biological tissue comprises thefollowing steps: providing a first solvent in a container; introducing asalt or an acid of a radioactive isotope into the first solvent suchthat the salt or acid disassociates into ionic components so as to forma first solution; introducing a second solvent into the first solutionso as to form a second solution; and introducing the medical device intothe second solution, wherein the ionic components migrate from thesecond solution into the molecular structure of the medical device.

In a preferred embodiment, a medical device for inhibiting ahyperplastic response in biological tissue generally comprises polymerichydrocarbon molecules forming the medical device and a salt or an acidof a radioactive isotope occluded within the polymeric hydrocarbonmolecules. As a result of this structure, the radioactive isotope in thepolymeric hydrocarbon molecules of the medical device inhibits ahyperplastic response in biological tissue.

Other systems, methods, features, and advantages of the presentinvention will be or will become apparent to one with skill in the artupon examination of the following drawings and detailed description. Itis intended that all such additional systems, methods, features, andadvantages be included within this description, be within the scope ofthe present invention, and be protected by the accompanying claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention can be better understood with reference to thefollowing drawings. The drawings are not necessarily to scale, emphasisinstead being placed upon clearly illustrating the principles of thepresent invention. Moreover, like reference numerals designatecorresponding parts throughout the several views.

FIG. 1 is a cut-away side view of the first step used in the method ofthe preferred embodiment.

FIG. 2 is a cut-away side view of the second step used in the method ofthe preferred embodiment.

FIG. 3 is a cut-away side view of the third step used in the method ofthe preferred embodiment.

FIG. 4 is a plan view of a mesh material of the preferred embodiment.

FIG. 5 is an exploded top depiction of the fibers of the mesh materialdepicted in FIG. 4.

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to conventional implantable medicaldevices that are designed to emit localized, low-level beta radiationwhile in or near biological tissue. The present invention also relatesto both a method of preventing hyperplasia in biological tissue graftsand a method of creating medical devices that accomplish this goal. Inother words, the present invention is a medical device having aradioactive element occluded within the molecular structure of themedical device, and a method of making the medical device. In thepresent invention, the radioactive element is not molecularly bonded tothe molecular structure of the medical device. Rather, as will bedescribed in detail below, the radioactive element is “trapped” withinthe molecular structure of the medical device.

Creation of the medical device of the present invention by the preferredmethod begins with the selection of a radioactive isotope to be occludedinto the molecular structure of the medical device. The preferredradioisotopes for the present invention are beta-emitting radioisotopeswith relatively long half-lives. For purposes of this disclosure, arelatively long half-life is generally considered any half-life inexcess of 150 days. Additionally, the preferred radioisotopes emit arelatively low level of beta radiation. For purposes of this disclosure,a low level of beta radiation is generally in the range of 10 uCi-1000uCi. Of course, one with skill in the art can readily determine theappropriate level of radiation to inhibit an undesired hyperplasticresponse. Such a level of radiation may not necessarily be within theabove-specified range, and the present invention is not meant to excludebeta radiation values outside of this range. The range of radiationvalues is only illustrative and preferred for the particular embodimentdescribed herein.

The following are examples of preferred radioisotopes Calcium 45;Chlorine 36; Prometheum 147; Strontium 90; and Technitium 99. All of theradioisotopes listed as examples have relatively long half-lives.Although radioisotopes with short half-lives may also be effective withthe present invention, a long half-life is preferred mainly due tostorage and shipping concerns. Over time, the quantity of radioactivityof a radioisotope will decrease due to nuclear decay. The half-life is ameasure of the rate of this decrease in radioactivity. If the quantityof radioactivity of the radioisotope decreases too rapidly, the medicaldevice must be used almost immediately after manufacturing. This leavesno time for shipping and no flexibility as to storage of the medicaldevice. For example, Prometheum 147, one of the above-listedradioisotopes, has a half-life of approximately 2.5 years. If Prometheum147 is selected for the present invention, the 2.5 year half-life wouldprovide ample time for manufacture, shipment, and storage. Then, whenthe medical device is needed, it still exhibits radioactive propertiesin adequate levels to provide the needed effect.

In the preferred embodiment 10 of the present invention, Calcium 45 isselected. Calcium 45 is preferred for a variety of reasons. To begin,Calcium 45 has a half-life of about 163 days. This length of half-lifeis long enough to allow shipment and storage of the medical device.However, the fact that the half-life is not several years means that themedical device will not continue to be radioactive for many years afterwhat is required to inhibit an undesirable hyperplastic response in apatient's biological tissue.

In the preferred embodiment 10 of the method described below, theradioactive isotope, Calcium 45, is not used alone. Rather, a salt or anacid of the radioisotope is preferred So, for example, the preferredisotope of Calcium 45 is used in the form of its salt, radioactiveCalcium Chloride (⁴⁵CaCl₂). Of course, Calcium 45 could also be used inits acid form, however, in the preferred embodiment described below,radioactive Calcium Chloride is preferred. The other radioisotopeslisted above can also be used in their salt or acidic form. For example,Chlorine 36 is used in the form of either radioactive Calcium Chloride(Ca³⁶Cl₂) or radioactive Hydrochloric Acid (H³⁶Cl) Prometheum 147 isused in the form of radioactive Prometheum Chloride (¹⁴⁷PmCl₃);Strontium 90 is used in the form of radioactive Strontium Chloride(⁹⁰SrCl₂); and Technitium 99 is used in the form of radioactiveTechnitium Fluoride (⁹⁹TcFl₅).

FIGS. 1-3 depict the preferred embodiment 10 of a method for creating aradioactive medical device according to the present invention. In FIG.1, a container 11 is depicted with a solvent 12 in the container 11. Thecontainer has a body portion 13 and a neck portion 14. Initially, thesolvent 12 is placed in the body 13 of the container 11.

The solvent 12 of the preferred embodiment 10 is a protic solvent. Morespecifically, the preferred protic solvent for the present invention isEthyl Alcohol (C₂H₅OH). Of course, other protic solvents may be used,such as ethyl acetate (CH₃COOC₂H₅) or toluene (C₆H₅CH₃). In the specificpreferred embodiment described herein, the amount of Ethyl Alcohol is0.5 milliliters. The amount of solvent 12 will generally vary with thesize of the medical device to be immersed in the radioactive solutionand other practical considerations. One skilled in the art will be ableto determine the appropriate amount of solvent 12 to be used for aspecific application.

Although glass is the preferred material of the container 11, othertypes of containers may be used. Generally, it is desirable to use acontainer 11 that is relatively non-reactive. Also, the shape ofcontainer 11 depicted in FIG. 1 is also not important to the presentinvention. Any shape will suffice, as long as the opening of thecontainer 11, as defined by the neck 14, is sufficiently large to accepta medical device to be exposed to a radioactive solution in thecontainer 11. As will be outlined below, the container 11 of thepreferred embodiment is also able to accept a lid, or to be sealed insome other way.

The preferred salt of a beta-emitting radioisotope, in this caseradioactive Calcium Chloride (⁴⁵CaCl₂) 16, is added to the Ethyl Alcohol12. See FIG. 1. In the preferred embodiment, 60 millicuries ofradioactive Calcium Chloride 16 is added into the container 11 andallowed to dissolve in the Ethyl Alcohol 12. In this way, the EthylAlcohol 12 serves to reduce the radioactive Calcium Chloride 16 intosolution. When introduced into the Ethyl Alcohol 12, the radioactiveCalcium Chloride 16 dissociates into its component ions: ⁴⁵Ca⁽⁺⁾ andCl⁽⁻⁾. The radioactive Calcium Chloride 16 will remain dissociated intosolution without any solid crystals in the container 11. Physically, theEthyl Alcohol 12 forms a type of matrix around the ⁴⁵Ca⁽⁺⁾ and Cl⁽⁻⁾ions in order to keep the ions dissociated in solution form.

The solution 17 formed by the radioactive Calcium Chloride 16 and theEthyl Alcohol 12 is depicted in the container 11 in FIG. 2. Once theradioactive Calcium Chloride 16 is dissolved into the Ethyl Alcohol 12,a second solvent 18 is added to the container 11, as depicted in FIG. 2.This second solvent 18 is preferably capable of expanding the molecularmatrix of a polymer structure. To this end, the preferred second solvent18 is Methylene Chloride (CH₂Cl₂). However, dimethylformamide andtetrahydrofuran would also function adequately, although they typicallydo not function as well as Methylene Chloride.

In the preferred embodiment 10, 19 milliliters of Methylene Chloride 18is added to the container 11 in batches of less than 5 milliliters at atime. In the preferred embodiment 10, a glass pipette 19 is used to holdand then dispense the 19 milliliters in four separate batches. In thisway, the Methylene Chloride 18 is slowly added to the solution 17 in thecontainer 11. The Methylene Chloride 18 is added slowly to the solution17 in order to prevent causing the ⁴⁵Ca⁽⁺⁾ and Cl⁽⁻⁾ ions to leavesolution and form crystals of radioactive Calcium Chloride along thebottom of the container 11.

The combination of Methylene Chloride 18 and the Ethyl Alcohol/CalciumChloride solution 17 form a new solution 21. Because Methylene Chloride18 and Ethyl Alcohol 12 are miscible fluids, the new solution 21 will bea blend of Methylene Chloride 18 and Ethyl Alcohol 12. Because the⁴⁵Ca⁽⁺⁾ and Cl⁽⁻⁾ ions are in ionic suspension within the Ethyl Alcohol12, the new solution 21 will generally comprise an homogenousdistribution of ⁴⁵Ca⁽⁺⁾ and Cl⁽⁻⁾ ions.

Once all the Methylene Chloride 18 has been added to the container 11, amedical device 22 to be exposed to the radioactive solution 21 is placedin the container 11. In the preferred embodiment 10, the medical device22 is a mesh material, as shown more clearly in FIG. 4. The meshmaterial 22 is preferably constructed of polypropylene. In use, amedical practitioner may wrap this polypropylene mesh 22, once it islabeled with a beta emitting radioactive substance, around a graft sitein order to bathe the site with beta radiation. The use of thisparticular medical device 22 will be described in greater detail below.

Of course, many different types of medical devices may benefit fromhaving the capacity to emit low level localized beta radiation, and thepresent invention is not intended to be limited to a polypropylene mesh.Generally, any place that a medical device with polymeric hydrocarbonmolecules may be used in a body, the advantages afforded by thecapability of emitting beta radiation may be helpful, For example, andwithout limitation, the medical devices of the present invention maycomprise: surgical sutures, stents, surgical patched, anti-thrombogeniccoatings, hydrophilic coatings, coverings or weavings over stents,fabric or mesh implants in the body, coatings on or woven into plasticcatheters (e.g. dialysis catheters), and ocular lens implants.

As noted above, in the preferred embodiments 10, the mesh 22 isconstructed of a polypropylene material. Polypropylene is abiocompatable material. However, in an alternative embodiment, the meshmaterial could be another biocompatable hydrocarbon material, such aspolyethylene, In another alternative embodiment, the mesh material couldcomprise a biodegradable material, such as Marlex™.

As depicted FIG. 3, the mesh 22 is placed in the solution 21. The mesh22 is preferably completely submerged within the solution 21. Once themesh 22 is placed in the container 11, a covering 23, or lid, is placedon the neck 14 of the container 11 in order to seal the container 11. Ifno lid 23 is used, the solution 21 will likely begin to evaporate, Thismay be undersirable if the mesh 22 is to stay in the solution 21 forseveral days.

Once the mesh 22 is in the solution 21, the Methylene Chloride 18 in thesolution 21 expands the polypropylene matrix 24 and the ⁴⁵Ca⁽⁺⁾ andCl⁽⁻⁾ ions begin migrating into and among the molecular structure 24 ofthe polypropylene mesh 22. The mesh 22 is left in solution 21 until thedesired concentration of radioactive Calcium is reached. In other words,the mesh 22 is left in solution 21 until it has incorporated the desiredlevel of radiation-emitting characteristics. The migration of theradioactive Calcium may take anywhere from a day, to several days, toseveral weeks. The length of time necessary for migration of theradioactive ions into the molecular structure of the mesh 22 depends onthe concentration of the radioactive ion present in the solution. In thepreferred example, a one inch square of polypropylene mesh 22 ispreferably left in the container 11 for 6-8 weeks.

One skilled in the art can readily determine the appropriate length oftime to expose the mesh 22 to the radioactive Calcium in the solution21. For example, small portions of the mesh 22 can be cut and tested todetermine the level of radiation emitted by the irradiated mesh 22. Ifthe level is too low, then the mesh 22 is left in solution 21. On theother hand, if the level of radioactive Calcium in the mesh 22 hasreached equilibrium, or the desired level of radioactivity, then themesh 22 is removed from the solution 21.

After reaching the desired concentration of radioactive material in themesh 22, the mesh 22 is removed from the container and permitted to dry.As the mesh 22 dries, the ⁴⁵Ca⁽⁺⁾ and Cl⁽⁻⁾ ions re-form radioactiveCalcium Chloride (⁴⁵CaCl₂) crystals 16, while still in the plastic mesh22. It should be recalled that the Methylene Chloride caused the plasticfibers 24 to swell when the mesh 22 was placed in the solution 21. Atthe same time the ⁴⁵ Ca⁽⁺⁾ and Cl⁽⁻⁾ ions are re-forming radioactiveCalcium Chloride 16, the drying process causes the polypropylene matrix24 of the mesh 22 to shrink back to its original shape. This shrinkagecauses the radioactive Calcium Chloride crystals 16 to become occludedin the polypropylene molecules 24. FIG. 5 depicts an exploded view ofone strand of the mesh 22 in order to demonstrate the occlusion of theradioactive Calcium Chloride 16 in the polypropylene fibers 24 of themesh 22. Thus, radioactive Calcium Chloride crystals 16 are dispersedthroughout the plastic polymer structure and held in place by thepolypropylene matrix 24.

In the preferred method 10, after drying is complete, the mesh 22 isrinsed several times with Ethyl Alcohol 16. Rinsing the mesh 22 removesany remaining Methylene Chloride 18 from the fibers and also removes anyradioactive Calcium Chloride molecules that are not trapped within themolecular structure 24 of the mesh 22. Rinsing the mesh 22 with EthylAlcohol 16 also serves to clean and sterilize the mesh material.

Ethyl Alcohol is not the only liquid that may be used to rinse the meshmaterial. If rinsing is desired, the mesh may be rinsed with a varietyof other solutions which are equally effective at removing MethyleneChloride and free radioactive ions. Of course, rinsing the mesh materialis not required by the present invention.

Generally, a solvent like Methylene Chloride will re-expand thepolypropylene fibers 24 of the mesh 22, thereby releasing theradioactive Calcium Chloride crystals 16. Water and bodily fluids aretypically not of this nature and will not re-expand the molecular chainstructure 24 of the polypropylene mesh 22 sufficiently to release theradioactive Calcium Chloride crystals 16. So, the radioactive calciumchloride molecules 16 stay trapped in the molecular structure 24 of themesh 22 and will not migrate out of the mesh 22 when the mesh 22 iseither handled or implanted into a patient's body.

The mesh 22 of the preferred embodiment 10 is typically used in surgicalprocedures in order to inhibit hyperplasia resulting from smooth musclecell proliferation, migration, and extracellular matrix deposition. Asnoted above, when biological tissue begins healing, an undesirablehyperplastic response may occur, such as intimal hyperplasia. The meshmaterial 22 of the preferred embodiment may be used to inhibit thisundesirable hyperplastic response.

In order to use the mesh 22 to inhibit an unwanted hyperplasticresponse, a surgeon typically wraps the mesh 22 of the preferredembodiment around a site where tissues have been grafted, such as by asuture. Once the mesh 22 is placed around the graft site, the surgeonsimply stitches the ends 26, 27 of the mesh 22 together in order tosecure it in place. Of course, anywhere biological tissues are graftedtogether, the mesh 22 of the preferred embodiment will be verybeneficial in preventing undesirable hyperplasia. For example, the mesh22 could be placed between the tissues to be grafted. In this way, thedevice holding the tissue together, such as a suture, would also securethe mesh 22 into place. One with skill in the art will be able to seemany additional uses for the medical device 22 of the preferredembodiment 10.

The method of incorporating radioactive material into a medical devicedescribed with regard to a polypropylene mesh 22 above could be usedsimilarly to radioactively label a whole host of medical devices. Suchdevices may include (without limitation): surgical sutures, stents,surgical patches, anti-thrombogenic coatings, hydrophilic coatings, acovering or weaving over stents, fabric or mesh implants in the body,coatings on or woven into plastic catheters (e.g dialysis catheters),and ocular lens implants. If one of these other medical devices areradioactively labeled by the above-described method, then theses deviceswill also inhibit undesirable hyperplasia.

If certain medical devices are used with the present invention, such assuture material for example, then it may be desirable to incorporate thepreferred salt of a radioactive isotope into a polymeric hydrocarbonmaterial before the medical device is actually made, or while the deviceis being made. For example, Calcium 45, or other beta emitting isotopecould be introduced into the polymeric hydrocarbon material during ablending or extruding process used to make the medical device.

It would be apparent to one skilled in the art that many variations andmodifications may be made to the preferred embodiments (i.e. preferrednonlimiting examples) as described above without substantially departingfrom the principles of the present invention. Such variations andmodifications are intended to be included herein and are within thescope of the present invention, as set forth in the following claims.

We claim:
 1. A medical device for inhibiting a hyperplastic response inbiological tissue, said medical device comprising: (a) polymerichydrocarbon molecules forming said medical device, wherein said medicaldevice comprises a mesh; and (b) a molecular form of a radioactiveisotope entrapped within a molecular structure of said medical device bythe molecular structure of said polymeric hydrocarbon molecules, whereinsaid radioactive isotope inhibits a hyperplastic response in biologicaltissue.
 2. The medical device of claim 1, wherein said polymerichydrocarbon molecules comprise polypropylene.
 3. A medical device forinhibiting a hyperplastic response in biological tissue, said medicaldevice comprising: (a) polymeric hydrocarbon molecules forming saidmedical device, wherein said polymeric hydrocarbon molecules comprise asynthetic polymer; and (b) a molecular form of a radioactive isotopeentrapped within a molecular structure of said medical device by themolecular structure of said polymeric hydrocarbon molecules, whereinsaid radioactive isotope inhibits a hyperplastic response in biologicaltissue.
 4. A medical device for inhibiting a hyperplastic response inbiological tissue comprising: (a) polymeric hydrocarbon molecules; and(b) a radioactive material interspersed within said hydrocarbonmolecules such that a molecular structure of said hydrocarbon moleculesencapsulates said radioactive material.
 5. The medical device of claim4, wherein said radioactive material comprises a salt of a radioactiveisotope.
 6. The medical device of claim 5, wherein said medical devicecomprises a mesh or sheet material.
 7. The medical device of claim 6,wherein said polymeric hydrocarbon molecules comprise polypropylene. 8.The medical device of claim 4, wherein said radioactive materialcomprises an acid of a radioactive isotope.
 9. The medical device ofclaim 8, wherein said medical device comprises a mesh.
 10. The medicaldevice of claim 9, wherein said polymeric hydrocarbon molecules comprisepolypropylene.
 11. A medical device comprising: (a) a material having amolecular structure capable of expansion through exposure to a solvent;and (b) a molecular form of a radioactive isotope trapped within saidmolecular structure of said material, wherein said molecular forminhibits a hyperplastic response in biological tissue.